Are you curious about how fast does tsunami travel? Tsunamis, also known as seismic sea waves, are a powerful and destructive natural phenomenon. TRAVELS.EDU.VN explains what determines their speed and how it impacts coastal regions. This guide will provide you with a comprehensive overview of tsunami speed, behavior, and safety measures.
1. Understanding Tsunamis: An Introduction
1.1. What is a Tsunami?
A tsunami is a series of extremely long waves caused by a large and sudden displacement of the ocean. These waves can travel across entire ocean basins and cause dangerous coastal flooding. Understanding the characteristics of tsunamis is crucial for coastal communities, allowing them to prepare for potential impacts and implement effective safety measures. This proactive approach can significantly reduce the risk of damage and loss of life when a tsunami strikes.
1.2. The Origin of the Term “Tsunami”
The word “tsunami” originates from the Japanese language, combining the characters for “harbor” (“tsu”) and “wave” (“nami”). This term aptly describes the devastating impact these waves often have on coastal harbors and communities. The international adoption of the term “tsunami” highlights the global recognition of this natural phenomenon and the importance of understanding its characteristics.
1.3. Tsunamis vs. Tidal Waves: Clearing the Confusion
While tsunamis are sometimes referred to as tidal waves, this is a misnomer. Tsunamis are seismic sea waves generated by sudden displacements in the ocean, whereas tides result from the gravitational pull of the Sun and Moon. It’s important to distinguish between the two, as tsunamis are unrelated to tides and can occur at any time, regardless of the tidal state.
1.4. Can Tsunamis Be Predicted? The Science of Early Warning Systems
Scientists can’t predict exactly when and where the next tsunami will strike, but Tsunami Warning Centers monitor seismic activity and can issue warnings when a tsunami is possible. Sophisticated forecast models predict wave height, arrival times, and flooding extent, helping to minimize the danger from an approaching tsunami. The combination of monitoring, modeling, and public awareness is essential for effective tsunami mitigation.
1.5. How Often Do Tsunamis Occur? A Look at Historical Data
Tsunamis causing damage or deaths near their source occur approximately twice per year, according to the Global Historical Tsunami Database. Distant tsunamis, which impact shores more than 1,000 kilometers away, happen about twice per decade. Understanding the frequency of these events helps in long-term planning and preparedness efforts for coastal regions.
1.6. Where Do Tsunamis Happen? Mapping Vulnerable Regions
Tsunamis can occur in any large body of water, but certain areas are more prone due to proximity to tsunami sources and ocean floor topography. The Pacific Ocean, particularly the “Ring of Fire,” experiences the majority of tsunamis. Areas like Japan, Russia, and Indonesia have historically seen a high percentage of these events.
1.7. Tsunami Hazard Levels in the United States: Assessing the Risks
An assessment of tsunami hazards in the United States indicates that any U.S. coast can be struck by a tsunami, but hazard levels vary by region. The U.S. West Coast, Southern Coast of Alaska, and Hawaii are at high to very high risk, while the U.S. Atlantic and Gulf Coasts have very low to low risk.
| Region | Hazard Level |
|---|---|
| U.S. West Coast | High to Very High |
| Alaska (Southern Coast) | High to Very High |
| Alaska Arctic Coast | Very Low |
| Hawaii | High to Very High |
| American Samoa | High |
| Guam and Northern Mariana Islands | High |
| Puerto Rico/U.S. Virgin Islands | High |
| U.S. Atlantic Coast | Very Low to Low |
| U.S. Gulf Coast | Very Low |
These hazard levels guide preparedness and mitigation efforts, ensuring that resources are allocated effectively to protect vulnerable communities.
1.8. Notable Tsunamis in U.S. History: Lessons Learned
Several damaging tsunamis have affected the United States, including local and distant events. These historical events underscore the need for continuous monitoring, improved warning systems, and public education to mitigate the impact of future tsunamis.
| Region | Local Tsunami* | Distant Tsunami* |
|---|---|---|
| U.S. West Coast | 1820, 1878, 1894, 1930 | 1946, 1952, 1957, 1960, 1964, 1975, 2006, 2010, 2011 |
| Alaska | 1788, 1845, 1853, 1900, 1917, 1946, 1957, 1958, 1964, 1994 | 1960 |
| Hawaii | 1868, 1975 | 1837, 1868, 1877, 1923, 1946, 1952, 1957, 1960, 1964, 2011, 2012 |
| American Samoa | 2009 | 1946, 1960 |
| Guam and Northern Mariana Islands | 1849 | — |
| Puerto Rico/U.S. Virgin Islands | 1867, 1918 | — |
* See question below: “What is the difference between a local and a distant tsunami?” To learn more, see the Historic Tsunami Calendar.
1.9. When Do Tsunamis Happen? The Unpredictable Nature of These Events
Tsunamis can occur at any time, regardless of the season or weather conditions. This unpredictability underscores the need for constant vigilance and preparedness in coastal areas.
1.10. Further Resources: Expanding Your Tsunami Knowledge
There are numerous online resources available for those who want to learn more about tsunamis. These resources include educational programs, safety websites, and historical databases. Key resources include the following:
- The COMET Program’s Tsunami Distance Learning Course
- National Weather Service’s JetStream Online Weather School
- National Weather Service’s Tsunami Safety website
- International Tsunami Information Center
- Global Historical Tsunami Database
- The TsunamiZone
2. The Science Behind Tsunamis: Causes and Mechanisms
2.1. What Triggers a Tsunami? Understanding the Primary Causes
Tsunamis are primarily caused by large and sudden displacements of the ocean. While earthquakes are the most common trigger, landslides, volcanic activity, weather events, and even near-Earth objects can also cause tsunamis.
2.2. How Earthquakes Generate Tsunamis: The Tectonic Connection
Earthquakes generate tsunamis through sudden movements of the water column. The location, magnitude, and depth of an earthquake are key factors. Most tsunamis are generated by earthquakes with magnitudes over 7.0 that occur under or very near the ocean, usually at subduction zones.
Examples of earthquake-generated tsunamis:
- March 11, 2011 Honshu Island, Japan
- December 26, 2004 Northern Sumatra, Indonesia
- March 27, 1964 Prince William Sound, Alaska
- April 1, 1946 Aleutian Islands, Alaska
- November 1, 1755 Lisbon, Portugal
- January 26, 1700 Cascadia Subduction Zone
2.2.1. Types of Earthquakes: Which Ones Are Most Likely to Cause Tsunamis?
Most tsunamis-generating earthquakes occur on thrust or reverse faults, where tectonic plates move toward each other in subduction zones. Strike-slip earthquakes, involving horizontal movement, can also generate tsunamis, often due to associated landslides.
2.2.2. The Largest Earthquake Ever Recorded: A Look at the 1960 Chile Earthquake
The largest earthquake ever recorded was a magnitude 9.5 earthquake off the coast of Southern Chile on May 22, 1960. This earthquake and the 1964 magnitude 9.2 earthquake in Prince William Sound, Alaska, both generated devastating tsunamis.
2.3. Landslides: Another Trigger for Tsunamis
Landslides, including rock falls, slope failures, and glacial calving, can generate tsunamis when they displace water. Landslide-generated tsunamis may be larger than seismic tsunamis near their source but typically lose energy quickly and rarely affect distant coastlines.
Examples of landslide-generated tsunamis:
- July 17, 1998 Papua New Guinea
- July 10, 1958 Southeast Alaska
- November 18, 1929 Grand Banks, Newfoundland, Canada
2.4. Volcanic Activity: Tsunamis from Below
Volcanoes, both above and below water, can generate tsunamis through pyroclastic flows, submarine explosions, caldera formation, and landslides. These volcanic tsunamis, like landslide tsunamis, usually lose energy quickly.
Examples of volcano-generated tsunamis:
- August 27, 1883 Indonesia
- May 21, 1792 Kyushu Island, Japan
- ~1610 BC Greece
2.5. Weather-Related Tsunamis: The Role of Air Pressure
Air pressure disturbances associated with fast-moving weather systems can generate “meteotsunamis.” These are similar to earthquake-generated tsunamis and depend on the intensity, direction, and speed of the air pressure disturbance.
Examples of meteotsunamis:
- June 13, 2013 Northeastern United States
- June 21, 1978 Vela Luka, Croatia
2.6. Near Earth Objects: A Rare Cause of Tsunamis
Although rare, near Earth objects like asteroids or comets can generate tsunamis. Large objects can cause “impact” tsunamis, while smaller objects that explode in the atmosphere can cause “airburst” tsunamis.
Example of a near Earth object tsunami:
- Chicxulub impact on Mexico’s Yucatán Peninsula
3. Unveiling Tsunami Characteristics: Speed, Size, and Behavior
3.1. How Many Waves Are There in a Tsunami? Understanding the Wave Train
A tsunami is not just one wave but a series of waves, often referred to as the tsunami wave train. A large tsunami may continue for days in some locations, with the time between wave crests ranging from approximately five minutes to two hours.
3.2. Decoding Tsunami Speed: Factors Influencing Velocity
The speed of a tsunami depends on the depth of the water it is traveling through. In the deep ocean, tsunamis can move as fast as a jet plane, over 500 mph, and can cross entire oceans in less than a day. As the waves enter shallow water near land, they slow to the speed of a car, approximately 20 or 30 mph.
Tsunami speed can be calculated using the formula:
Speed = √(water depth * acceleration of gravity)3.3. How Big Is a Tsunami? From the Deep Ocean to the Shoreline
In the deep ocean, tsunami waves may be barely noticeable, rarely more than three feet high, with wavelengths of hundreds of miles. As they enter shallow water, their wavelengths decrease, they grow in height, and currents intensify. Most tsunamis are less than 10 feet high when they strike land, but in extreme cases, they can exceed 100 feet.
3.4. What Does a Tsunami Look Like When It Reaches the Coast?
When a tsunami reaches the coast, it may appear as a fast-rising flood or a wall of water (bore). It will not look like a normal wind wave. Sometimes, the water will suddenly recede, exposing the ocean floor.
3.5. How Long Does a Tsunami Last? The Duration of the Threat
Large tsunamis may continue for days in some locations, reaching their peak often a couple of hours after arrival and gradually tapering off. Dangerous tsunami currents can persist for days.
3.6. Local vs. Distant Tsunamis: Understanding the Difference
Local tsunamis originate close to the coast and may arrive in less than one hour, posing the greatest danger due to limited warning time. Distant tsunamis are generated far away, allowing more time to issue and respond to warnings.
3.7. Tsunamis vs. Normal Ocean Waves: Key Distinctions
Tsunamis differ from normal ocean waves in several ways, including their source, the location of energy, wavelength, wave period, and wave speed. Tsunamis move through the entire water column, while wind waves only affect the ocean surface.
| Feature | Tsunami | Wind Wave |
|---|---|---|
| Source | Earthquakes, landslides, volcanic activity, certain types of weather, near earth objects | Winds blowing across the ocean surface |
| Location of Energy | Entire water column | Ocean surface |
| Wavelength | 60-300 miles | 300-600 feet |
| Wave Period | 5 minutes – 2 hours | 5-20 seconds |
| Wave Speed | 500-600 miles per hour (in deep water)20-30 miles per hour (near shore) | 5-60 miles per hour |
4. Detecting and Forecasting Tsunamis: The Science of Early Warning
4.1. Tsunami Warning Centers: Responsibilities and Operations
The NWS operates two Tsunami Warning Centers that monitor observational networks, analyze earthquakes, evaluate water-level information, issue tsunami messages, conduct public outreach, and coordinate with other organizations to improve operations.
4.2. How Are Tsunamis Detected? A Network of Sensors
Tsunami Warning Centers rely on seismic and water-level networks to detect tsunamis. These networks include seismic networks, Deep-ocean Assessment and Reporting of Tsunami (DART) systems, and coastal water-level stations.
4.3. DART Systems: Real-Time Tsunami Detection in the Deep Ocean
DART (Deep-ocean Assessment and Reporting of Tsunami) systems are used for early detection, measurement, and real-time reporting of tsunamis in the open ocean. These systems consist of a bottom pressure recorder (BPR) and a surface buoy that relays data via satellite.
4.4. Coastal Water-Level Stations: Monitoring Ocean Height Near the Shore
Coastal water-level stations collect information about the height of the ocean at specific coastal locations. This data is relayed to the warning centers and used to confirm tsunami arrival time and height.
4.5. Tsunami Forecasting: Predicting the Path and Impact
Tsunami forecasting involves analyzing earthquake information, running tsunami forecast models, and incorporating data from seismic and water-level networks. These models simulate tsunami movement and estimate coastal impacts.
5. Understanding Tsunami Messages: Warnings and Alerts
5.1. Tsunami Messages: Communicating the Threat
Tsunami messages are issued by the Tsunami Warning Centers to notify emergency managers, local officials, the public, and other partners about the potential for a tsunami. There are four levels of tsunami alerts: warning, advisory, watch, and information statement.
5.1.1. Tsunami Warning: Imminent Danger
A tsunami warning is issued when a tsunami with the potential to generate widespread inundation is imminent, expected, or occurring. It alerts the public that dangerous coastal flooding and powerful currents are possible.
5.1.2. Tsunami Advisory: Potential Hazards
A tsunami advisory is issued when a tsunami with the potential to generate strong currents or waves dangerous to those in or very near the water is imminent, expected, or occurring.
5.1.3. Tsunami Watch: Preparing for Possible Impact
A tsunami watch is issued when a tsunami may later impact the watch area. Emergency management officials and the public should prepare to take action.
5.1.4. Tsunami Information Statement: Monitoring the Situation
A tsunami information statement is issued when an earthquake or tsunami has occurred of interest to the message recipients, often to indicate there is no threat of a destructive basin-wide tsunami.
5.2. Tsunami Threat Message: International Alerts
A tsunami threat message is a tsunami message for international partners in the Pacific and Caribbean. These messages help national authorities understand the threat to their coasts.
5.3. Who Issues Tsunami Messages?
The Tsunami Warning Centers prepare and issue tsunami messages for their respective designated service areas. Primary recipients include NWS Weather Forecast Offices, state emergency operations centers, and the U.S. Coast Guard.
5.4. Canceling Tsunami Messages: Declaring Safety
The Tsunami Warning Centers issue a cancellation after determining that a destructive tsunami will not affect an area or that a tsunami has diminished to a level where additional damage is not expected.
5.5. Tsunami Warning Center Service Areas: Mapping Responsibility
The National Tsunami Warning Center in Palmer, Alaska, serves the continental United States, Alaska, and Canada. The Pacific Tsunami Warning Center in Honolulu, Hawaii, serves the Hawaiian Islands, the U.S. Pacific and Caribbean territories, and the British Virgin Islands.
5.6. Determining Alert Levels: A Comprehensive Analysis
Tsunami Warning Centers base initial tsunami messages on preliminary earthquake information. Subsequent messages are based on impact estimation resulting from additional seismic analysis, water-level measurements, tsunami forecast model results, and historical tsunami information.
5.7. Message Issuance Speed: Rapid Response Times
The time it takes for a Tsunami Warning Center to issue a tsunami message depends on the seismic network density and distribution near the earthquake’s point of origin. In regions of high seismic network density, messages can be issued within five minutes.
5.8. Receiving Tsunami Messages: Staying Informed
In the United States, tsunami messages are broadcast through local radio and television, marine radio, wireless emergency alerts, NOAA Weather Radio, NOAA websites, and social media accounts.
6. Tsunami Safety: Preparing for and Responding to a Tsunami
6.1. Why Are Tsunamis Dangerous? Understanding the Threats
Tsunamis can produce unusually strong currents, rapidly flood land, and devastate coastal communities. Low-lying areas such as beaches, bays, lagoons, harbors, and river mouths are the most vulnerable.
6.2. How to Prepare for a Tsunami: Proactive Measures
To prepare for a tsunami:
- Educate yourself about tsunami warnings and ensure you have multiple ways to receive official warnings.
- Make an emergency plan that includes plans for family communication and evacuation.
- Map out routes from home, work, and other places you visit often to safe places on high ground or inland.
- Practice walking your routes.
- Put together a portable disaster supplies kit.
6.3. Recognizing Tsunami Warnings: Official and Natural Signs
Tsunami warnings can be official, broadcast through various media, or natural, including strong earthquakes, a loud roar from the ocean, and unusual ocean behavior.
6.4. Responding to a Tsunami Warning: Immediate Actions
If you are in a tsunami hazard zone and receive an official tsunami warning, stay out of the water, get more information, and evacuate if officials ask you to. If you receive a natural tsunami warning, take action immediately and move to high ground.
6.5. Issuing Evacuation Orders: Local Authority
Evacuation requests/instructions are typically issued and coordinated by local emergency management officials. In Hawaii, the Pacific Tsunami Warning Center decides whether evacuations are necessary for local earthquakes.
6.6. Seeking Safety in Tall Buildings: Vertical Evacuation
Most buildings are not designed to withstand tsunami impacts, but the upper stories of some strong and tall buildings may provide protection if no other options are available.
6.7. Boating During a Tsunami: Safety at Sea
If you are on a boat during a tsunami warning, your response will depend on your location. In a harbor, leave the boat and move to a safe place on land. At sea, move to a safe depth and stay away from harbors under warning.
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An official tsunami warning sign indicates the importance of community preparedness and evacuation planning in coastal areas.
